Those fusible-link PROMs had an abnormally high failure rate, particularly during programming/verification. Once programmed, they were generally considered to be as "bomb-proof" as any monolithic hardware. The relatively low yields were an issue for the production people, so they weren't as popular as one might have hoped.

The problem, of course, was that they were touchy to program, and made-in-the-kitchen programmers, even if built along the lines recommended by the PROM vendors (NSC, TI, Signetics, MMI, et al), often didn't work well. They were often used as logic devices, similar to PALs. PROMs were not as fast as TTL, nor were they as fast as RAM, but they fit a niche that nothing else would fit. Eventually, their high failure rate and the low cost of EPROMs and EE-PALs drove them off the market.

RE